Backdoor Roth IRA Calculator
Calculate backdoor Roth conversion with pro-rata rule. See tax cost if traditional IRA has balance.
By Konstantin Iakovlev · Updated September 2026 · Source: IRS — Instructions for Form 8606 (Nondeductible IRAs)
Tax-Free Conversion
$7,500.00
Taxable Amount
$0.00
Tax Cost
$0.00
Pro-Rata Calculation
| Existing Pre-Tax IRA Balance | $0.00 |
| New Contribution (after-tax) | $7,500.00 |
| Total IRA Balance | $7,500.00 |
| Pro-Rata Percentage | 0.00% |
| Taxable on Conversion | $0.00 |
| Tax-Free on Conversion | $7,500.00 |
| Tax Cost (24% bracket) | $0.00 |
Use the Backdoor Roth IRA Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.
Disclaimer: This calculator is for informational purposes only and does not constitute tax, financial, or legal advice. Results are estimates based on the information you provide and current rates. Always consult a qualified tax professional or financial advisor for advice specific to your situation.
How It Works
Converting traditional IRA funds into a Roth IRA looks simple on paper, but the tax bill depends heavily on whether you already hold pre-tax money in any traditional IRA. The pro-rata rule treats all of those balances as a single pool, and that pooling is what determines how much of your conversion the IRS counts as taxable.
To find the taxable portion, the tool applies the pro-rata formula: (Total Pre-Tax IRA Balance / Total Traditional IRA Balance) * Converted Amount. The amount converted is the year's non-deductible contribution, $7,500 or $8,600 at 50 and over, and the taxable share is taxed at the federal bracket you pick (22% to 37%), giving you an estimate of what the move will cost.
The most frequent error is leaving out traditional IRA balances spread across separate accounts, since the IRS aggregates every one of them, SEP and SIMPLE IRAs included, when applying the pro-rata rule, and it uses their combined value on December 31 of the year you convert, not the balance on the day of the conversion. Knowing your current marginal tax bracket also matters here, because an off bracket throws off the entire tax-cost estimate.
Example: Backdoor Roth with $50,000 Already in a Rollover IRA
- 1 Input: $50,000 of pre-tax money in a rollover IRA (its value on December 31 of the conversion year), the $7,500 under-50 contribution made non-deductible and converted to a Roth IRA, and the 24% federal bracket.
- 2 Pro-rata share: the pre-tax money is $50,000 of the $57,500 total, or 86.96%. That share of the $7,500 conversion is taxable: $7,500 × $50,000 ÷ $57,500 = $6,521.74.
- 3 Result: only $978.26 converts tax-free, and the tax cost is $6,521.74 × 24% = $1,565.22.
- 4 With a $0 pre-tax balance the whole $7,500 would convert tax-free. Rolling the $50,000 into an employer 401(k) that accepts roll-ins before December 31 takes it out of the calculation, because Form 8606 counts only traditional, SEP and SIMPLE IRA balances at year-end.
Source: IRS — Instructions for Form 8606 (Nondeductible IRAs) · Last updated: September 2026
Frequently Asked Questions
How does a backdoor Roth IRA conversion work?
What is the pro-rata rule for backdoor Roth?
Is the backdoor Roth still legal in 2026?
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